I read this article recently in Lancet. It concerns an investigation into the mysterious deaths of children in India who ate lychees. As you can see from the article the children were dying from severe hypoglycemia caused by hypoglycin A which blocks glycogenesis. The susceptable children consumed the lychees and then didn't eat dinner. For most people going without dinner isn't going to kill them because the body can make its own glucose from protein and fat but hypoglycin A shuts this process (gluconeogenisis) down. With this process blocked the children couldn't produce their own glucose and when their glucose supplies ran out they couldn't replenish them without eating, so they became severely hypoglycemic and died.